1. Field of the Invention
The present invention relates to a data transmission apparatus for transmitting data between a camera module and an electronic information apparatus connected to the camera module and particularly for transmitting data between an image display device (i.e. a display device) of a mobile communication terminal apparatus and a camera module, as well as a data reception apparatuses for receiving data transmitted by the data transmission apparatus, a data transmission and reception apparatus including the data transmission apparatus and the data reception apparatus, and a data transmission and reception method.
2. Description of the Related Art
Generally speaking, in digital cameras and digital video cameras, for example, conversion from optical images to electric signals is realized with the use of image sensors (e.g. Charge Couple Devices (CCD) or Complementary Metal Oxide Semiconductors (CMOS)). Each of the elements that constitute such an image sensor is a plate including small and regularly-arranged picture elements (pixel units which are also referred to as a detector matrix) that are sensitive to light and colors. The resolution level of such a detector matrix varies depending on its physical size and its degree of integration. Generally speaking, an image sensor includes hundreds of thousands or more pixels that are two-dimensionally arranged in a matrix.
With regard to the manufacturing process of such image sensors, it is possible to integrate a digital electronic apparatus and an image sensor that is an analog electronic apparatus on one semiconductor device with the use of CMOS techniques which are highly developed. Further, due to reduction in the size and weight of camera modules, it is possible to mount a camera module in a smaller electronic information apparatus, such as a portable computer or a portable mobile communication terminal apparatus in each of which a camera module is integrated.
For example, when a camera module is mounted on a portable computer or a portable mobile communication terminal apparatus, a large number of output lines are required for image signals output from the camera module. This situation where a large number of output lines are required poses a big problem in dealing with wiring problems of digital image signals, data transmission problems, unnecessary radiant noise problems, and in the endeavor of reducing the costs and electric power consumption of the terminal apparatuses and the systems as well as of making the apparatuses and the system compact.
As an example of a digital data transmission and reception method to solve these problems, Japanese Laid-open Publication No. 2002-218455 discloses an LVDS (Low Voltage Differential Signal) serial transmission and reception method for accurately transferring digital image signals, which is shown in FIG. 6.
FIG. 6 is a block diagram that shows an example of a configuration of the main part of a conventional digital data transmission and reception circuit.
As shown in FIG. 6, the digital data transmission and reception circuit 100 includes a data transmission apparatus 101 for transmitting data and a data reception apparatus 111 for receiving the transmitted data. Because data is transmitted and received this way, it is not necessary to have a large number of output lines for the image signals output from the data transmission apparatus 101, unlike the example mentioned above.
The data transmission apparatus 101 includes a supply voltage Vin input unit 103 for controlling the circuit 102, an input unit 104 for receiving transferred bit elements, output units 105 and 106 for transferring non-inverted current signals and inverted current signals, and a resistor 107 for setting an external current.
The data reception apparatus 111 includes a supply voltage Vin input unit 113 for controlling the circuit 112, input units 114 and 115 for receiving non-inverted current signals and inverted current signals, an output unit 116 for outputting bit elements from received current signals, and a resistor 117 for setting an external gain.
In such a case, data transfer is performed by the data transmission apparatus 101 and the data reception apparatus 111 which operate with a supply voltage of a mobile communication terminal apparatus (the supply voltage being, for example, 1.5 V to 1.8 V as compared to a typical LVDS supply voltage being approximately 3.0 V) and use current signals of sub-LVDS type; however, the arrangement may not be limited to this example.
Signals are transferred from the data transmission apparatus 101 to the data reception apparatus 111 via the transfer lines 118 and 119, with the use of a self-biased signal transfer method in accordance with FIG. 6. According to this self-biased signal transfer method, a resistor 120 (for example, with a resistance value of 100 ohm) is provided between the transfer lines 118 and 119.
FIG. 7 shows the waveform pattern of the transfer lines 118 and 119 from the data transmission apparatus 101 to the data reception apparatus 111. It should be noted that the operational principle here is not different from that of a normal LVDS circuit.
As shown in FIG. 7, an electric signal in the transfer lines 118 and 119 is interpreted as one bit in the case where the voltage waveform of the transfer line 118, which is a non-inversion line, is positive. In such a case, the voltage waveform of the transfer line 119, which is an inversion line, is negative. Likewise, an electric signal is interpreted as 0 (zero) bit in the opposite situation. Using a pair made up of a current signal transmitter and a current signal receiver that are of sub-LVDS type makes it possible to achieve a high data-transfer rate, while electromagnetic noises are kept at a minimum level.
The following describes an example of image data output by the data transmission apparatus 101 from a camera module to an image display device, using image data for a VGA size as an example.
In image data for a VGA size, data for 640 pixels are included per line, and data for 480 lines are included per frame. In many cases, the data size for one pixel is 8 bits to 14 bits, depending on the bit number that is obtained when a signal from an image pickup element is quantified as a digital value. According to a conventional technique, image data output from a camera module to an image display device requires that one frame is dealt with in units of a number of lines. FIG. 8 shows an example of a data sequence in serial transmission and reception, which is used as a method of identifying in which frame, image data belongs to one of such lines.
In FIG. 8, the starting end of a frame is indicated by a synchronization code FS (Frame Starting end) 201, and the ending end of the frame is indicated by a synchronization code FE (Frame Ending end) 202. Thus, the frame is fixed using the special synchronization codes. Within such a frame, image data and statistical data for each line also has a synchronization code LS (Line Starting end) 203 indicating the starting end of the record and a synchronization code LE (Line Ending end) 204 indicating the ending end of the record. Here, the statistical data is, for example, accumulated luminosity values and is used for controlling the exposure so that the display screen gets darker when it is too bright or the display screen gets brighter when it is too dark.
In the present situation, the frame starting end synchronization code 201 is transferred and followed by image data for the first line 205 and the line ending end synchronization code LE 204. Further, the line starting end synchronization code LS 203 is followed by image data for the second line 205 and the line ending end synchronization code LE 204. In this manner, image data 205 for one of lines 1 through 480 is transferred between a line starting end synchronization code LS 203 indicating the starting end of the line and a line ending end synchronization code LE 204 indicating the ending end of the line. Further, after the image data 205 for the final line, which is the line 480, and the line ending end synchronization code LE 204 are transferred, the line starting end synchronization code LS 203 is transferred, and then statistical data SD 206 is transferred. Subsequently, after the statistical data SD 206 is transferred, a frame ending end synchronization code FE 202 which indicates the ending end of the transferred frame is transferred.
The statistical data amount of statistical data SD 206 may be smaller or larger than the data amount in one image data line. Thus, in correspondence with this, there is a possibility that the final line may be shorter or longer. It is, however, very unlikely that a problem arises because of this situation. The reason is because as the starting end of a frame is indicated by a synchronization code FS 201, and the ending end of a frame is indicated by a synchronization code FE 202, the frame is fixed with the use of special synchronization codes that do not appear in image data. With this arrangement, it is possible to easily separate, on the reception side, the image data 205 for the lines 1 through 480 and the statistical data SD 206 from a data sequence, on an assumption that within one frame, 480 data units of image data that are separated from one another by synchronization codes are included, and also the 481st data unit includes the statistical data SD 206. Furthermore, in the case where it is understood in advance that no statistical data SD 206 exists, it is possible to separate, on the reception side, the 480 data units of image data 205.
According to the conventional LVDS (Low Voltage Differential Signal) serial transmission and reception method disclosed in Patent Document 1 mentioned above, it is possible to have effects of realizing image signals output by a camera module with a smaller number of wirings and of solving the problems by reducing unnecessary radiant noises, reducing the costs and electric power consumption of the system, and making the system compact; however, in order to easily separate image data 205 for each frame and each line without failure, and to easily separate the image data 205 from the statistical data SD 206 following the image data 205 without failure, it is necessary to use the frame starting end synchronization code FS 201 and the frame ending end synchronization code FE 202, as well as the line starting end synchronization code LS 203 that indicates a starting end of each line within the frame, and the line ending end synchronization code LE 204 that indicates the ending end of each line, which are special synchronization codes that do not appear in the image data 205. Thus, it is necessary to insert synchronization codes before and after the image data 205 for each line and the statistical data SD 206 to be inputted to the input unit 104 of the data transmission apparatus 101, and it is also necessary to detect the synchronization codes that are present before and after the image data 205 for each line and the statistical data SD 206 to be output from the output unit 116 of the data reception apparatus 111, and to separate the synchronization codes from other data such as the image data 205 and the statistical data SD 206; therefore, it is necessary to provide a synchronization code inserting circuit at a stage prior to the data transmission apparatus 101 and to provide a synchronization code separating circuit at a stage after the data reception apparatus 111. Consequently, this arrangement is not appropriate because it requires further improvement in order to make transmission and reception faster and to make the transmission and reception timing control circuit smaller in size.
The present invention aims to solve the problems of the conventional technique that are mentioned above, and particularly with regard to LVDS data transmission and reception between a camera module and an electronic information apparatus, aims to provide a data transmission apparatus, a data reception apparatus that receives data from the data transmission apparatus, a data transmission and reception apparatus and a data transmission and reception method in which these apparatuses are used, with which it is possible to easily and accurately recognize the positions of image data, such as the starting end and the ending end of one frame and the starting end and the ending end of image data for one line, as well as the starting end and the ending end of data for one pixel without increasing the data amount in serial transmission, with the use of multiplexing processing and separation processing of image data and synchronization codes, and also to make such data transmission and reception faster and to make a transmission and reception timing control circuit smaller in size.